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The quality of French sperm is on the decline. But a new study released this week has raised the question of whether the one-third drop in French men's sperm count in recent years is linked to the production of the country's most famous export: wine.

In a follow up to a groundbreaking 2012 study that revealed French men's sperm count plummeted by about one-third from 1989 to 2005, the researchers' latest investigation has raised the question of whether France's wine industry may be partly to blame.

The new study, which involved 26,600 men, shows how the decline in sperm quality has been more acute in certain regions of France.

The two areas which have seen the steepest drops were found to be the regions of Aquitaine and Midi-Pyrénées in south-western France, which also happen to be two centres for French wine production, notably the famous Bordeaux labels. (See map below)

The French researchers behind the study say those two regions are home to some of country's largest number of farm workers, many of whom are likely to be exposed to pesticides - which researchers say are the chief culprit for the decline in sperm quality. The chemicals can disrupt the men's hormones and thus interrupt sperm production, the study found.

"Wine cultivation is the activity that uses the most pesticides in proportion to the agricultural area," Institut de Veille Sanitaire researcher Dr. Joëlle Le Moal, who helped carry out the study, said.

"In these two regions there could be a local contributor due to the pesticides they use in wine cultivation, becasue this kind of production uses so much," Le Moal told The Local.

As part of the follow-up study that was published this week they took a look at how the decline varied across France and spotted the sharp drop off in south-western France.

In addition to a decrease in sperm count, from the late 1980s to the mid-2000s men in Aquitaine and Midi-Pyrénées also had a lower than average number of properly shaped sperm cells. Over the same period regions like Franche-Comté and Brittany actually saw an increase.

Yet there were no obvious health problems in the men of both south-western French regions that would readily explain the gap. They are not particularly obese, the rates of alcohol and tobacco consumption aren’t higher than their neighbours - hence the reason they have pointed the finger at the use of pesticides.

However, other famous wine growing regions like Burgundy and the Loire Valley in central France do not seem to be as affected by the drop in sperm quality, as the map below suggests. Aquitane and Midi-Pyrenees are the areas shaded dark red.

Le Moal and her colleagues first hinted at this correlation in their December 2012 study that showed sperm count had dropped by 32.2 percent from 1989 to 2005 in French men. The drop the researchers uncovered was about 1.9 percent per year.

The concentration of sperm for a man aged 35 dropped on average from 73.6 million sperms per milimetre in 1989 to 49.9 in 2005, the scientists found.

Le Moal stressed on Friday the concern behind the findings.

"We concluded at the time that this constituted a public health warning , not just in terms of fertility outcomes, but also because sperm quality is co-related to life expectancy," she told The Local.

Le Moal says the study is the most important ever carried out in France and "probably throughout the world" but more research was needed.

"It is very important to monitor the quality of sperm at international level now that we have data showing its deterioration in France," Le Moal told The Local.